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'[pic]: Can you amplify with a single 2n2222 ??'
2002\02\10@143612 by rad0

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I am trying to drive a piezo speaker using a pic
and I want to amplify my output, or just make it
louder.

I am making a little tone generator for a tabletop
oven that will sound when the thing stops.  It has
a built in timer, but no bell to let you know the
thing has stopped.

So, using what amounts to the Freqout command from
a stamp, I generate my tone, but it isn't loud enough.

Can you make a little amplifier using a single 2n2222 transistor?

Any help appreciated.

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2002\02\10@144227 by David VanHorn

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>
>Can you make a little amplifier using a single 2n2222 transistor?

Certainly. Look up class-A amplifiers.
Alternatively, you can use the transistor as an open collector driver,
which is a class-C amplifier.


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2002\02\10@144819 by Dave Dilatush

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rad0 wrote...

>I am trying to drive a piezo speaker using a pic
>and I want to amplify my output, or just make it
>louder.
>
>I am making a little tone generator for a tabletop
>oven that will sound when the thing stops.  It has
>a built in timer, but no bell to let you know the
>thing has stopped.
>
>So, using what amounts to the Freqout command from
>a stamp, I generate my tone, but it isn't loud enough.
>
>Can you make a little amplifier using a single 2n2222 transistor?

Sure, no problem at all.

Take your 2N2222 transistor and connect its emitter lead to ground.
Connect the base lead to one end of a 10K resistor, and connect the
other end of this resistor to the PIC output pin.  Connect one end of
your piezo to ground, and the other end of the piezo to the collector
lead of the 2N2222.  From the 2N2222 collector connect a 1K resistor to
your +5V supply voltage.

If the loudness problem was that the PIC was having trouble driving the
piezo's low impedance, this will solve the problem.  If it doesn't help,
try connecting the top end of that 1K resistor to a higher DC voltage to
get more output.

Keep in mind that most of these piezo elements are **VERY** frequency
sensitive: drive them with too low or too high a frequency and you can
barely hear them; drive them exactly at their resonant frequency and
they can be ear-splitting.  
You may want to experiment with the frequency, to make sure this isn't
in fact the source of your problem; I never have any trouble getting
good volume from one of these things, even when driven right from a PIC
pin, so long as I use the right frequency.

Hope this helps a bit...

Dave

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2002\02\10@150035 by rad0

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let me give this a try - thanks

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2002\02\10@150927 by Thomas C. Sefranek

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Certainly!

That's what transistors do!

You will need a higher voltage source to drive the collector. (12V)
A simple common emitter amplifier will drive a Piezo.
You might also look into driving the Piezo directly with two pic output pins
and push-pull it for twice the drive.


rad0 wrote:

{Quote hidden}

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2002\02\10@151529 by Dave Dilatush

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You wrote...

>let me give this a try - thanks

You're welcome.

One thing you might try is to hook up your piezo to the output of an
audio signal generator and sweep the frequency around until you find the
loudest output; then replicate this same frequency with your PIC.
Worked for me...

Dave

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2002\02\10@151943 by Spehro Pefhany

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At 01:34 PM 2/10/02 -0800, you wrote:
>So, using what amounts to the Freqout command from
>a stamp, I generate my tone, but it isn't loud enough.
>
>Can you make a little amplifier using a single 2n2222 transistor?

Well, sure, but I bet that's not the problem. The PIC has
a fair bit of output drive for a piezo (which basically looks
like a ~10n capacitor (depending on size).

Try this: Try driving *two* port pins 180' out of phase,
and connect the piezo across them. This gives you double the
P-P voltage across the piezo. Higher supply voltage will help
with both the output drive and the loudness. Make sure the
PIC supply is well bypassed.

Best regards,

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2002\02\10@153309 by Mahmood Elnasser

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Is your piezo contained in a little plastic box or is it just a lose
plate ?
The box makes resonance and amplifies the sound a lot with resonance
frequency depending on size and shape of box.

{Original Message removed}

2002\02\10@154633 by David VanHorn

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At 01:59 PM 2/10/02 -0800, rad0 wrote:
>let me give this a try - thanks


If you have a pair of output pins, you can do a bridge drive, but be careful.
You want to take both pins to the same state, before taking them to
opposite states.

00,01,11,10,00... rather than 10,01,10...

The reason is that with the second sequence, you make a capacitive voltage
doubler, and are sinking large current pulses into the protection diodes,
risking CMOS latchup.



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2002\02\10@162227 by rad0

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lots of good suggestions, thanks everyone.

I changed the prgram around to step thru some frequencies and
found a more correct freq.  And this will be ear splitting enough
for my purposes.

I thought the little piezo tranducer would act like a speaker, but I
see now that is not really true.

I have been trying different combinations of frequencies and different
durations
and different rates of repeating the tone.  If you repeat it fast enough, it
sort of
rings. - the dog seems to really hate that  ;-)

the amp isn't really necessary, but it worked fine with a higher voltage

I'm going to try the 180 out of phase technique and the push pull next.  -
but it's
already loud enough

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2002\02\10@165222 by David VanHorn

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At 03:20 PM 2/10/02 -0800, rad0 wrote:
>lots of good suggestions, thanks everyone.
>
>I changed the prgram around to step thru some frequencies and
>found a more correct freq.  And this will be ear splitting enough
>for my purposes.

Most of these are resonant at 2700 Hz, which for some reason is the point
where human hearing works the best.

>I thought the little piezo tranducer would act like a speaker, but I
>see now that is not really true.

It's response curve would put most rollercoasters to shame.

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2002\02\11@035520 by Michael Rigby-Jones

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{Quote hidden}

You could do the push-pull using the proposed 2N2222 transistor.  Configure
the transistor on common emitter mode as sugested with a 1k collector load.
Then connect PIC pic to the transistor base via a 10k resistor and also to
one side of the piezo.  The other side of the piezo goes to the transistor
collector.

Mike

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2002\02\11@094206 by Jim

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  "Alternatively, you can use the transistor as an
   open collector driver, which is a class-C amplifier."

I don't get it.

Maybe I'm from the old school where Class C amps
were only used for RF (I can't recall a single audio
application for a stage biased Class C and conduction
angle for each cycle was significantly less than
180 degrees) where the tank circuit provides for the
balance of the re-creation of the waveform (tank, or
LC resonant circuits being analogous to balance wheels
or tuning forks of sorts).

The "open coll." app above sounds more like the 2n2222 is
being used as a switch, perhaps in PWM mode as in
class D or the like.

Jim



{Original Message removed}

2002\02\11@122332 by David VanHorn

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At 08:41 AM 2/11/02 -0600, Jim wrote:
>    "Alternatively, you can use the transistor as an
>     open collector driver, which is a class-C amplifier."
>
>I don't get it.
>
>Maybe I'm from the old school where Class C amps
>were only used for RF

Where does RF start, exactly?
Connect an antenna to it.

>(I can't recall a single audio
>application for a stage biased Class C and conduction
>angle for each cycle was significantly less than
>180 degrees) where the tank circuit provides for the
>balance of the re-creation of the waveform (tank, or
>LC resonant circuits being analogous to balance wheels
>or tuning forks of sorts).

Probably because they were worried about fidelity.
If you're driving a beeper, fidelity is right out the window.
You can drive a beeper as part of a resonant circuit, with the beeper
acting as a lossy tank capacitor.

>The "open coll." app above sounds more like the 2n2222 is
>being used as a switch, perhaps in PWM mode as in
>class D or the like.

You could do that too.

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2002\02\11@124440 by Jim

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I would, in the future, tend to shy away from
the classification of an 'amplifier' stage as
Class A, B or C unless that stage were truly
working as an amplifier with specific bias set
up so as to actually attain a particular bias
and hence operate as a Class A, B or C stage - this
is as opposed to a single device operated as a
simple on/off switch in some sort of pulse width
modulation mode.

As to where RF begins - that's easy. Does it involve
'radio frequencies' and the technologies classically
employed to modulate, amplify, detect, filter,
demodulate or radiate EM energy as opposed to 'audio
frequencies' which have in past decades normally
'modulated' an RF carrier in order to transmit
intelligence though the ether from point A to point
B?

I'm afraid today's 'digi-head' has blurred all
distinction between the two ...

Jim

{Original Message removed}

2002\02\11@125724 by Martin Peach

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----- Original Message -----
From: "Jim" <RemoveMEjvpollspam_OUTspamKILLspamDALLAS.NET>
To: <RemoveMEPICLISTTakeThisOuTspamspamMITVMA.MIT.EDU>
Sent: Monday, February 11, 2002 12:43 PM
Subject: Re: [pic]: Can you amplify with a single 2n2222 ??


...
> As to where RF begins - that's easy. Does it involve
> 'radio frequencies' and the technologies classically
> employed to modulate, amplify, detect, filter,
> demodulate or radiate EM energy as opposed to 'audio
> frequencies' which have in past decades normally
> 'modulated' an RF carrier in order to transmit
> intelligence though the ether from point A to point
> B?

Audio is ELF. An audio-frequency circuit still radiates electromagnetic
waves, just not very efficiently.

>
> I'm afraid today's 'digi-head' has blurred all
> distinction between the two ...

The boundary _is_ very fuzzy, but most animals can't hear beyond about
200kHz...

/\/\/\/*=Martin

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2002\02\11@131236 by Jim

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  "Audio is ELF. An audio-frequency circuit still radiates
   electromagnetic waves, just not very efficiently."

Very incorrect in all but perhaps a very few ill-designed
products. Most of us responsible for actual RF design
don't call possible 'spuriuous emissions of AF energy' over
100 dB down from a 'box' "radiation of electromagnetic
waves". Leakage flux perhaps (as from a power xfmr) - but
not 'radiation'.

I realize I'm addressing a majority digi-head crowd - some
of this discussion is only underscoring that point.

No offense meant to any digi-head on the list. We couldn't
possibly do what we do in the field of RF today without uC's
or the talented programmers and designers who actually make
those devices 'sing' and 'dance' ...

Jim



{Original Message removed}

2002\02\11@132549 by Martin Peach

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----- Original Message -----
From: "Jim" <EraseMEjvpollspamspamspamBeGoneDALLAS.NET>
To: <RemoveMEPICLISTKILLspamspamMITVMA.MIT.EDU>
Sent: Monday, February 11, 2002 1:12 PM
Subject: Re: [pic]: Can you amplify with a single 2n2222 ??


>    "Audio is ELF. An audio-frequency circuit still radiates
>     electromagnetic waves, just not very efficiently."
>
> Very incorrect in all but perhaps a very few ill-designed
> products. Most of us responsible for actual RF design
> don't call possible 'spuriuous emissions of AF energy' over
> 100 dB down from a 'box' "radiation of electromagnetic
> waves". Leakage flux perhaps (as from a power xfmr) - but
> not 'radiation'.

Sorry. I meant the electrical part of the amplifier, not the sound waves.
Should have said "an audio-frequency circuit will emit extreme low frequency
electromagnetic radiation as a side effect of its functioning."

/\/\/\/*=Martin

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2002\02\11@132559 by David VanHorn

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>
>No offense meant to any digi-head on the list. We couldn't
>possibly do what we do in the field of RF today without uC's
>or the talented programmers and designers who actually make
>those devices 'sing' and 'dance' ...

Why does it matter to you, wether the output is to an antenna, or a resistor?

If I drive a parallel combination of L and C, with an "open collector"
transistor, using pulses that are shorter than half the oscillation period,
that looks like "class C" to me.

The fact that the signal is propagated to air by the capacitor, rather than
to the aether by the inductor, makes no difference to the transistor.

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2002\02\11@145131 by Aaron Lahman

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All my text-book charts list Audio up to 20 kHz.. anything above that is
listed as RF.  :)

It's an artificial distiction if you ask me.  On any grounded linear amp
circuit I make, i can pick up 60 Hz 'RF' if i don't filter it well and am
working near my non-sheilded wall-wart power supply :)

-Aaron

> {Original Message removed}

2002\02\13@095903 by Bourdon, Bruce

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   "Audio is ELF. An audio-frequency circuit still radiates
    electromagnetic waves, just not very efficiently."

"Very incorrect in all but perhaps a very few ill-designed
products. Most of us responsible for actual RF design
don't call possible 'spuriuous emissions of AF energy' over
100 dB down from a 'box' "radiation of electromagnetic
waves". Leakage flux perhaps (as from a power xfmr) - but
not 'radiation'.

I realize I'm addressing a majority digi-head crowd - some
of this discussion is only underscoring that point.

No offense meant to any digi-head on the list. We couldn't
possibly do what we do in the field of RF today without uC's
or the talented programmers and designers who actually make
those devices 'sing' and 'dance' ...

Jim"

Jim, others:

I'm afraid your not quite correct here Jim; as stated by others, there is no
magic frequency where AF ends and RF begins - it is most definitely blurred.

What is important is Efficiency, as efficiency for each purpose varies with
frequency.

But there definitely are audio frequency "RF" transmitters, and these are
not "ill-designed products." For example, the U.S. Navy uses what most would
consider as "Audio Frequencies" in their equipment designed to communicate
with submerged submarines. Though efficiency is horrendous, the importance
of the task makes the inefficiencies acceptable.

Also, you should not assume that the audience cannot rationally consider the
topic, as many have mixed disciplines. While I probably could not match your
level of expertise, I have been workinging with RF as an amateur (HAM) since
the '70s. I'm sure there are many readers that have even more experience
than I.

Bruce.

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2002\02\13@101518 by Spehro Pefhany

picon face
At 09:59 AM 2/13/02 -0500, you wrote:

>But there definitely are audio frequency "RF" transmitters, and these are
>not "ill-designed products." For example, the U.S. Navy uses what most would
>consider as "Audio Frequencies" in their equipment designed to communicate
>with submerged submarines. Though efficiency is horrendous, the importance
>of the task makes the inefficiencies acceptable.

The ELF transmitters in northern Russia, Michigan and Wisconsin are
almost *beneath* the audio range (< 100Hz!).

Here's one take on it:-

http://www.provcomm.net/pages/joe/introlf.htm

"The "long wave" spectrums of frequencies are divided into three main
grouping by convention. These are;
LF (Low Frequencies) 535 to 150 kHz
VLF (Very Low Frequencies) 150 kHz to 3 kHz
ELF (Extremely Low Frequencies) 3 kHz to 300 cycles (approx.)"

Best regards,

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2002\02\13@104737 by Thomas C. Sefranek

face picon face
Spehro Pefhany wrote:

> At 09:59 AM 2/13/02 -0500, you wrote:
>
>> But there definitely are audio frequency "RF" transmitters, and these
>> are
>> not "ill-designed products." For example, the U.S. Navy uses what
>> most would
>> consider as "Audio Frequencies" in their equipment designed to
>> communicate
>> with submerged submarines. Though efficiency is horrendous, the
>> importance
>> of the task makes the inefficiencies acceptable.
>
>
> The ELF transmitters in northern Russia, Michigan and Wisconsin are
> almost *beneath* the audio range (< 100Hz!).

NONSENSE!  They are <100KHz!

{Quote hidden}

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2002\02\13@110825 by Michael Rigby-Jones

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> -----Original Message-----
> From: Thomas C. Sefranek [SMTP:EraseMEtcsspamEraseMECMCORP.COM]
> Sent: Wednesday, February 13, 2002 3:46 PM
> To:   @spam@PICLIST@spam@spamspam_OUTMITVMA.MIT.EDU
> Subject:      Re: [pic]: Can you amplify with a single 2n2222 ??
>
> NONSENSE!  They are <100KHz!
>
>
Technically you are correct, they are <100KHz,  but also <100Hz!

Have a look at

http://web.tiscali.it/vlfradio/zevs/zevs.htm
http://hypertextbook.com/facts/2001/LisaWu.shtml

Regards

MIke Rigby-Jones

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2002\02\13@112051 by Spehro Pefhany

picon face
At 10:46 AM 2/13/02 -0500, you wrote:

>>The ELF transmitters in northern Russia, Michigan and Wisconsin are
>>almost *beneath* the audio range (< 100Hz!).
>
>NONSENSE!  They are <100KHz!

Hard to argue with that, as 82Hz (the Russian frequency) and 76 Hz (the
American frequency) are both < 100Hz AND (way) < 100kHz. ;-)

Here's a page, direct from the US navy on the Wisconsin transmitter:

http://enterprise.spawar.navy.mil/spawarpublicsite/docs/fs_clam_lake_elf.pdf

There is another "band" below ELF, called ULF that starts around 30Hz, but
I don't know if it has any practical use.

Best regards,

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